I own a copy of this bag (and the 17L Lowepro - way too big for what you want to carry btw). This is a nice small bag that I think might work for you. I measured mine and it is pretty much what they say. The nice thing is that it is small and you can organize the inside how you like. There are extra pockets and the top can be zipped shut or just flapped shut with velcro for easy access.
I got mine for half this but it was used.
http://www.amazon.com/Pentax-85115-Adventure-Gadget-DSLR/dp/B004EHZDX4
I recently went on a trip and had my DA 70 Limited, my DA 40 Limited and my DA 15 Limited as well as my 1.4x HD TC and a battery grip and my K3 in this bag. I currently have it configured with no dividers and I'm using it for my K3 with DA* 200 and occasionally I'll toss a limited prime in the end pouch to add to the fun. I can toss the DA 40 and the 1.4x TC in the end pouch and still have no problems carrying it. 40/56/200/280 is not a bad set of focal lengths for a small kit. I've carried my 18-135 and two primes as well. It's fairly versatile.